Low permeable refractory and method of making the same



Aug. 23, 1932. F. .1. TONE 1,873,071

LOW PERMEABLE REFRACTORY AND METHOD OF MAKING THE SAME Original Filed Aug. 10. 192'! INVENTOR FRANK JEROME TONE BY $44M. C- mm/Ma ATTORNEY Patented Aug. 23, 1932 i WE FRANK JEROME TONE, OF NIAGARA FALLS, NEW YORK, ASSIGNOR TO THE CAR- so jifnD't'r'M' COMPANY, or NIAGARA FALLS,- NE 'YOR'K, A corvroRAs'rIoN or emu LOWiPERMEABL'E,REFRACTQRY AND METHOD OEVMAKING SAME Coptinuatiqn of application Serial No 212,139, filed August 10, 1927 This application filed May 26, 1.93% I Serial Nq 455,716.

This invention relates mPPOYd. frectorynrticles, phrticularly those composed of silicon carbide,- an d to a method bf'p'r'o carbide, Wherethe grain is oxidized at high temperatures. The penetration of both gases and slugs into the pores oflthe material greatly accelerates its destruction.

While the closing of the .pores' at the surface'of the brickby' Vairioiis meatns, such es those described iii United States Patent No.

-1,473,286 to EwBLFor'se} offers so'me relief in' 'thisrespect the relief istemporary and the adyantage is lost as'soonflas the original. facing of the brick-Has been destroyed to'a very slight depth. My improvedf process in- .volves the pro'dubtion of a non-permeable structure, extending throughout the the refi zictory aiid independent of any surface glazing, although the presence (Sf-the latter may alsobe desirable. 1 In the manufacture of a non-permeable re frectory, Ltake a suitable mixture .of :grits and'loond-in accordance With-any of thevarious practices Well known in the art, such as described in the United States Patents, 'Njos. v-'-77'2, 262-and 1204,5211 issued .to Tone and? 1;4'9f26--issued to Beecher. Hoieifever, I .em-f

ployjzi type of grain which. has been submitted to a rocess which I shall designate as mulling I define mulling as the iprocess of removing the ough corners from the grain and breakingiip the needle shaped llrarticlesv p inte s. witheek gr atly 4 e: ducing, the ,aive'r gi grainsizepi he ate ia -la 'llie. mullingi peratiqn s? s n; my

4%? process... of; mak ng QJ i tQRY vst-i s from the ,usu&l :-0p- T? i ilru hing fidi grinding. Ingnind g. i' stm e n. ube; mill; for; .exanip e,." hi eyfi yfidr h Such h spfifidthat the pebbles are; cerried zto the, top -of .;the mill; b cent iiugal; orge;

whereupon they drop by the action of grav- 1 it: tbjproduetlie grindin OECr'ushing efFect 'w tho'ut contact Wi'th"th fj nhte'lfial" on the" sides ge'f tnej inill' until they zittfhe'bo tto'm of their'fill. The dg'reeto which 1m '55 ticl'effsf are criished in amill such es a tube mill or hell fill ll depends pri'nisirilyfiipoh theen- I ergy 'which is possessed by the ba'llsbr peb ble s' fit the time of 'irnpact. If this energy issufliciently greet, 'the pn'rticle Inay be com- 130 pletely crushed, but if th eene rgy' is some what less; the particle may merely fre ctui'e along a plane of'mechaniearweaknesfbr chip at the edges or at sharp projecting cornei s In mullir ig, the niill' isi'oteted rate, ew speed i r er' hatthfpe s ail be 'sinoothed I and the splinters broken by' the action usually known as attrition. i In the pr'efei ied method pf carrying out d my process; the material is first 6'1 wherefthe par'ticlesczih be smoothed land" bi ought to a in" iegulitr shape "'b mttri tion. an 'eX let used, the inilli. being r" tated such a? i:ate met th rnz telriel slides doifin'th' sides of the mill i qn'tfa ftj with; the "pebbles Without 'cafs ceding: Y The corners 'offthe pa'rticleis 'arei tlll l S worn off, and the splihters broken with; outfapprecizibly'effecting the ayeia gegri iin size. "If ;1 tube mill is used for the mulling op; eretion the mill is rote-ted'at 'approxiinate ly ttyo thirds the speedcreme ordiher ly used for rushing; As an ira'mpleh speed. i

02? I15 :6 2"( l ,r'eyoluti ons per isi'nupeis sufligient f e f iill s i hsij i li te iwd id normally operate'elt 25 "to 3G moles -i s per i Ininuteforcrushing or feed is" preferihly somewhat lesser th in th us uel 1 crushing of grinding p eretions, and he al p bb i 'y'. eo ie fie e i rth 'n 9$.. c it j sm g 'ByT dii -SF m itheconditi'ohs ee -describes asses-'1 s v5 ppsi l e s m e ai n n; heres w ners endsharp edges sire" broken oil, and in; whi h th splinters {are brakes up and the number of 5 irregular" "shipped particles re diic'd'to aiminimilm. 1

In the drawing,

Figure 1 shows the approximate path of the balls or pebbles in the usual crushing operation in a ball or tube mill,

Figure 2 illustrates the path of the pebbles during the mulling operation,

Figure 3 shows the particles of silicon car- .bide grain after they have been crushed and screened to a particular grain size or mesh, and

Figure 4 shows the particles of silicon carbide grain after they have been mulled and screened to the same mesh as the" particles shown in Figure 3.

In the mulled grain the dimensions are nearly equal'in all directions, while the grain which has not been mulled contains grain with irregular corners and projections, as well as flat or plate-like pieces. In screening,

the particles of irregular shape often pass" through the meshes of the screen even, when their .dimensionsin certain directions'considerably exceed themesh size. For this reason a mulled grain usually gives the appearance of a somewhat smaller mesh grain than one which has not been mulled, even when both are carefully graded to the same mesh.

The conditions necessary for mulling as here 'defined will depend upon the toughness of the individual particles or grains. Con ditions which would mull a material such as silicon carbide or aluminum oxide might result in an appreciable reduction in grain size with certain ma'terials having a 'lesser degree of toughness or resistanceto impact. These conditions can be controlled to a great extent by variations in the speed of the mill, rate of feed, and size or weight of the pebbles or other means used for crushing.

I have found that by mulling the grain previous to the bonding together of the particles to form a refractory, the permeability to gases of the resulting product is greatly reduced. The particles, owing to their reg ular shape, can be consolidated to a more dense material than is the case when grain that has not been mulled is used, even though the grit sizes are the same in both cases. The process is especially applicable to the manufactiire of refractory articles made from silicon carbide, although it may also be used in the case of crystalline aluminum oxide and other similar grain.

Care should be taken that the bond used is itself not permeable. With silicon carbide refractories this condition is approached with a close firing clay of the ball type, or with numerous other combinations of ceramic bonds and fluxes which do not react with one another or with silicon carbide in such a way as to form a vesicular structure. The desired structure is most closely approached, however, by using a bond of about fine silicon carbide. V

The following examples from test records are given to show the efiect of mulling the grain on the permeability of the refractory. The figures in each caserepresent an average of a number of brick made in the same way, all of which closely approach the average value.

Permeability Sample No. Grain Bond 7 Without Glazed .glaze Not mulled J A 35 i 350 7 Not mulled A 335 d A 18 38 A 18 B 305 725 ,B 365 860. B 140 185 B 95 x175 These data show clearlythe value ofzmulled grain in reducing permeability, and that this. effect is independent'of the surface glaze;

The additional value of using a refractory made from mulled grain in combination with a glaze is also shown. In the examples above noted, it will be seen that the permeability of is defined by the following method. For evaluati'ng the permeability of a brick, I use a de-' vice whereby the brick to be tested is supported broad face down on an annular feltgasket supporting its outer edge in an ironconta'iner, and the space between the .sides of the brick" and walls of the container is filled with mer-.

cu'ry, while the brick is held in position by a .105 weight supported on it in such away as not.

to prevent the passage of gas through: the face Y of thebrick.

With the brick in this apparatus,iair.is

passed through it from thegasket outward at such a ratethat the drop in pressure across the brick amounts to 2".of water. When: this condition has been established, the rate of flow is determined by asuitable capillary tubeflow-meter inserted in the air line ahead of a value for standard ing by where t is the thickness of thebric'k in inches. The unit of permeability is defined as the" number of cubic centimeters per minute flowing through the '9" X 4 faceof astandard;

size brick under a difference of pressure of 2 inches of water.

precision of i 5% orbetter. By useof this apparatusthe perme'abilities of bricks, even This method of measurement gives a readily duplicable value with'a those containing different amounts and different types of bond, may be readily compared.

It will be understood that the permeability unit used throughout this specificiation and the annexed claims is a unit determined as herein described.

Although the invention has a special advantage when used with an oxidizable grain, such as silicon carbide, it is also advantageous in the case of refractories made from crystalline aluminum oxide, sillimanite or other similar materials. Because of the needle-like crystals present in sillimanite, the mulling process for producing a dense refractory is es pecially applicable.

claim: 1. A silicon carbide refractory made principally of mulled silicon carbide grain. 2. The process of manufacturing a silicon carbide refractory which comprises mulling a substantial proportion of the silicon carbide grain, mixing the mulled grain with a. binder, forming and burning the mix. 3. A furnace lining formed of silicon carbide made of mulled silicon carbide grain and a binder.

4. A burned refractory silicon carbide article containing in its composition, silicon carbide grains which have been ground down and rounded to the extent that the mix packs together to form a body, which, when burned has a permeability of less than 250 units.

5. The process of making a refractory article of low permeability which comprises grinding a refractory material to the desired grit size, dry mulling the refractory material after it has been ground to wear off the sharp corners produced in the grinding operation by attrition without further material reduction in the grain size, thereafter packing and shaping the mix containing the mulled grains, and burning the chafed article.

6. As a new article of manufacture, a silicon carbide refractory having a low permeability comprised principally of silicon carbide grains and grains which have been ground from a mass of silicon carbide to the desired grit size, and have thereafter been mulled, and having a higher density than an article of similar dimension and composition formed of grains which have not been mulled.

In testimony whereof I aflix my signature.

FRANK JEROME TONE. 

